Aminotransferases, also known as transaminases (E.C.2.6.1) catalyze the transfer of an amino group, a pair of electrons, and a proton from a primary amine of an amino donor substrate to the carbonyl group of an amino acceptor molecule.
A general transaminase reaction is shown in Reaction I, below. In this reaction, an amino acceptor (keto, or ketone) which is the precursor of the desired amino acid product, is reacted with an amino donor. The transaminase enzyme exchanges the amino group of the amino donor with the keto group of the amino acceptor. The reaction therefore results in the desired chiral amine product and a new amino acceptor (keto) compound, which is a by-product.

An exemplary stereoselective transamination by a transaminase is demonstrated by the activity of transaminase from Arthrobacter sp. KNK168 on 3,4-dimethoxyphenylacetone (see e.g., Iwasaki et al., 2006, Appl. Microbiol. Biotechnol. 69: 499-505; and U.S. Pat. No. 7,169,592, each of which is hereby incorporated by reference herein). Thus, transaminase enzymes have potential industrial use for stereoselective synthesis of optically pure chiral amines and the enantiomeric enrichment of chiral amines and amino acids (Shin et al., 2001, Biosci. Biotechnol. Biochem. 65:1782-1788; Iwasaki et al., 2003, Biotech. Lett. 25:1843-1846; Iwasaki et al., 2004, Appl. Microb. Biotech. 69:499-505, Yun et al., 2004, Appl. Environ. Microbiol. 70:2529-2534; and Hwang et al., 2004, Enzyme Microbiol. Technol. 34: 429-426). Chiral amines play an important role in the pharmaceutical, agrochemical and chemical industries. Chiral amines are frequently used as intermediates or synthons for the preparation of various pharmaceuticals, such as cephalosporin or pyrrolidine derivatives. Examples of the use of aminotransferases to generate useful chemical compounds include: preparation of intermediates and precursors of pregabalin (e.g., WO 2008/127646); the stereospecific synthesis and enantiomeric enrichment of β-amino acids (e.g., WO 2005/005633); the enantiomeric enrichment of amines (e.g., U.S. Pat. Nos. 4,950,606, 5,300,437, and 5,169,780); and the production of amino acids and derivatives (e.g., U.S. Pat. Nos. 5,316,943, 4,518,692, 4,826,766, 6,197,558, and 4,600,692). Hence, transaminases are useful for the enantiomeric enrichment and stereoselective synthesis of chiral amines.